DNA/RNA in a Y-shaped nanochannel

ABSTRACT

A mechanism is provided for ratcheting a double strand molecule. The double strand molecule is driven into a Y-channel of a membrane by a first voltage pulse. The Y-channel includes a stem and branches, and the branches are connected to the stem at a junction. The double strand molecule is slowed at the junction of the Y-channel based on the first voltage pulse being weaker than a force required to break a base pair of the double strand molecule. The double strand molecule is split into a first single strand and a second single strand by driving the double strand molecule into the junction of the Y-channel at a second voltage pulse.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of U.S. patent application Ser. No. 13/724,041, entitled “BASE-BY-BASE RATCHETING OF DNA/RNA IN A Y-SHAPED NANOCHANNEL”, filed on Dec. 21, 2012, which is incorporated herein by reference in its entirety.

BACKGROUND

The present invention relates to nanopore/nanochannel devices, and more specifically, to capture and control of molecules in nanopore/nanochannel devices.

Nanopore sequencing is a method for determining the order in which nucleotides occur on a strand of deoxyribonucleic acid (DNA). A nanopore (also referred to a pore, nanochannel, hole, etc.) can be a small hole in the order of several nanometers in internal diameter. The theory behind nanopore sequencing is about what occurs when the nanopore is submerged in a conducting fluid and an electric potential (voltage) is applied across the nanopore. Under these conditions, a slight electric current due to conduction of ions through the nanopore can be measured, and the amount of current is very sensitive to the size and shape of the nanopore. If single bases or strands of DNA pass (or part of the DNA molecule passes) through the nanopore, this can create a change in the magnitude of the current through the nanopore. Other electrical or optical sensors can also be positioned around the nanopore so that DNA bases can be differentiated while the DNA passes through the nanopore.

The DNA can be driven through the nanopore by using various methods, so that the DNA might eventually pass through the nanopore. The scale of the nanopore can have the effect that the DNA may be forced through the hole as a long string, one base at a time, like thread through the eye of a needle. Recently, there has been growing interest in applying nanopores as sensors for rapid analysis of biomolecules such as deoxyribonucleic acid (DNA), ribonucleic acid (RNA), protein, etc. Special emphasis has been given to applications of nanopores for DNA sequencing, as this technology holds the promise to reduce the cost of sequencing below $1000/human genome.

SUMMARY

According to an embodiment, a method for ratcheting a double strand molecule is provided. The method includes driving the double strand molecule into a Y-channel of a membrane by a first voltage pulse. The Y-channel includes a stem and branches, and the branches are connected to the stem at a junction. The method includes slowing the double strand molecule at the junction of the Y-channel based on the first voltage pulse being weaker than a force required to break a base pair of the double strand molecule, and splitting the double strand molecule into a first single strand and a second single strand by driving the double strand molecule into the junction of the Y-channel at a second voltage pulse.

According to an embodiment, a system for ratcheting a double strand molecule is provided. The system includes a membrane with a Y-channel, and the Y-channel includes a stem and branches, where the branches are connected to the stem at a junction. The system includes a top fluidic chamber on one side of the membrane and a bottom fluidic chamber on an opposing side of the membrane. A first voltage pulse of a voltage source drives the double strand molecule into the Y-channel of the membrane. The double strand molecule is slowed at the junction of the Y-channel based on the first voltage pulse being weaker than a force required to break a base pair of the double strand molecule. A second voltage pulse of the voltage source drives the double strand molecule into the junction of the Y-channel to split the double strand molecule into a first single strand and a second single strand.

Additional features and advantages are realized through the techniques of the present invention. Other embodiments and aspects of the invention are described in detail herein and are considered a part of the claimed invention. For a better understanding of the invention with the advantages and the features, refer to the description and to the drawings.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

The subject matter which is regarded as the invention is particularly pointed out and distinctly claimed in the claims at the conclusion of the specification. The forgoing and other features, and advantages of the invention are apparent from the following detailed description taken in conjunction with the accompanying drawings in which:

FIG. 1 is a cross-sectional view of a DNA-ratcheting nanodevice according to an embodiment.

FIG. 2 is an abbreviated version of the nanodevice in which a membrane includes two Y-channels according to an embodiment.

FIG. 3 illustrates a time-dependent biasing electric field chart to ratchet a DNA molecule through the Y-channel according to an embodiment.

FIG. 4 is an abbreviated version of the nanodevice with sensors in the left and right branches to respectively sequence single strand DNA molecules according to an embodiment.

FIG. 5 is a method of ratcheting a double strand molecule through a Y-channel according to an embodiment.

FIG. 6 is an abbreviated version of the nanodevice in which the membrane has Y-channels with multiple branches according to an embodiment.

FIG. 7 is a block diagram that illustrates an example of a computer (computer test setup) having capabilities, which may be included in and/or combined with embodiments.

DETAILED DESCRIPTION

Sequencing DNA at an affordable cost has inspired many new DNA sequencing methods. However, one existing technical challenge is to control the motion of DNA at a single-nucleotide resolution. Without such control, some nucleotides could be read multiple times while some others could be missed during a sequencing process. Therefore, it is desirable to have a device that can nucleotide-by-nucleotide (i.e., base-by-base) ratchet DNA. Nature has built a small yet efficient DNA-ratcheting machine: DNA polymerase is a protein molecule which controls a directional motion of DNA nucleotide-by-nucleotide. DNA polymerase is used in a sequencing technology based on an existing method. To mimic the ratcheting process by the DNA polymerase, a man-made DNA-ratcheting machine is provided herein using synthetic nanomaterials. According to an embodiment, a nanodevice has a Y-shaped nanochannel (e.g., a Y-channel) to electrically drive a double-stranded DNA (dsDNA) into the stem channel, followed by electrically unzipping of the dsDNA and threading each single-stranded DNA (ssDNA) through a branch channel.

Now turning to the figures, FIG. 1 is a cross-sectional view of a DNA-ratcheting nanodevice 100 according to an embodiment. A Y-channel 140 is embedded in a membrane 101, and the Y-channel 140 is a Y-shaped nanochannel. A double strand DNA molecule (dsDNA) 110 is being driven through and unzipped in the Y-channel 140 as discussed further herein. The membrane 101 may be a solid state membrane, such as, e.g., SiO₂, Si₃N₄, and/or another insulating material. The membrane 101 may have a thickness of 100 nm. Generally, a channel can be a nanopore through a solid membrane or a surface channel in a typical nanofluidic device (such as a lab-on-chip) as understood by one skilled in the art.

One kind of Y-channel 140 is the Y-shaped carbon nanotube (Y-CNT) as shown in FIG. 1. Several methods have been developed to fabricate Y-shaped CNTs which have been designed to transfer and multiply charge signals at molecular level (molecular signal transduction).

Further information regarding Y-shaped carbon nanotubes is discussed in the following articles which are herein incorporated by reference: Papadopoulos C, Rakitin A, Li J, Vedeneev A S, Xu J M (2000) Electronic transport in Y-junction carbon nanotubes. Phys Rev Lett 85:3476. Deepak F L, Govindaraj A, Rao CNR (2001) Synthetic strategies for Y-junction carbon nanotubes. Chem Phys Lett 345:5-10. Tu Y, Xiu P, Wan R, Hu J, Zhou RH, and Fang HP (2009), Water-mediated signal multiplication with Y-shaped carbon nanotubes, Proc. Natl. Acad. Sci. 106, 18120-18124.

In the DNA-ratcheting nanodevice 100, two fluidic chambers (cis. and trans.) 130 and 135 are separated by the solid membrane 101 and connected to one another by the Y-channel 140. The top fluidic chamber 130, the bottom fluidic channel 135, and the Y-channel 140 are all filled with an electrically conductive solution 145. The electrically conductive solution 145 is an electrolyte solution as understand by one skilled in the art.

The Y-channel 140 (Y-CNT) has a stem 170 connected to left branch 172 and right branch 174. FIG. 2 illustrates an abbreviated version of the nanodevice 100 in which the membrane 101 includes two Y-channels 140. It is noted that multiple Y-channels 140 may be formed in the membrane 101.

Although understood to be present, FIG. 2 shows the nanodevice 100 without the double strand DNA molecule 110 and the fluidic chambers 130 and 135 so as not to obscure the figure. Example dimensions of the Y-channel 140 are provided below. The stem 170 may have a width 205 (and/or diameter) of 4 to 10 nm (nanometers) and/or sub ten nanometers. The left branch 172 may have a width 210 (and/or diameter) of 2 to 4 nm and/or sub 5 nanometers. The right branch 174 may have a width 212 (and/or diameter) of 2 to 4 nm and/or sub 5 nanometers. The angle 250 of a junction 220 may be 30 to 120 degrees, to form the left and right branches 172 and 174.

With reference to FIG. 1, a voltage source 106 is connected to electrode 108 a in the top fluidic chamber 130 and connected to electrode 108 b in the bottom fluidic chamber 135. The voltage source 106 (along with ammeters 160 and 165 in FIG. 4) may be implemented in and/or controlled by a computer test setup 700 discussed in FIG. 7. Voltage pulse V₀ of the voltage source 106 is applied to the electrodes 108 a and 108 b which results in a biasing electric field E₀ being applied across the membrane 101, by inserting the two electrodes 108 a and 108 b into cis. and trans. chambers, respectively. The electrodes 108 a and 108 b may be Ag/AgCl electrodes connected to a battery or any direct current voltage source (e.g., the voltage source 106).

The (negatively charged) dsDNA molecule 110 can be electrophoretically driven into the stem 170 of the solid-state Y-channel 140 by the voltage pulse V₀ applied by the voltage source 106. When the dsDNA molecule 110 arrives at the junction 220 (shown in FIG. 2) of the Y-channel 140, a higher biasing electric field E₁ (i.e., a higher voltage pulse V₁ is applied by the voltage source 106) is utilized to overcome the energy barrier for unzipping one base-pair of the dsDNA molecule 110, for breaking two base-stacking, and for rotating the dsDNA segment by 36 degree (the angle between neighboring base-pairs in dsDNA). Particularly, the higher voltage pulse V₁ (resulting in the higher electric field E₁) breaks the dsDNA molecule 110 into ssDNA 112 in the left branch 172 and into ssDNA 114 in the right branch 174 of the Y-channel 140, when the dsDNA molecule 110 is driven (forced) into the sharp end of the junction 220.

Accordingly, once the dsDNA molecule 110 is driven through the stem 170 to the junction 220 by the electric field E₀ (via the voltage pulse V₀), the dsDNA molecule 110 (temporarily) stops (or slows) at the junction 220. Then, the higher electric field E₁ (via the voltage pulse V₁) is applied, which is strong enough to break (i.e., overcome the energy barrier for unzipping) the base pair of the dsDNA molecule 110 that is positioned at (abuts) the junction 220. After the voltage pulse V₁ is applied by the voltage source 106 while the dsDNA molecule 110 abuts the junction 220, the dsDNA molecule 110 unzips (i.e., the base pair is broken) into the ssDNA molecule 112 and ssDNA molecule 114 respectively in branches 172 and 174. The ssDNA molecule 112 has a chain of single bases (connected by a DNA backbone), and the ssDNA molecule 114 has a chain of single bases (connected by a DNA backbone), as understood by one skilled in the art.

FIG. 3 illustrates a time-dependent biasing electric field chart 300 to ratchet the DNA molecule 110 through the Y-channel 140 according to an embodiment. The y-axis shows the electric field E, and the x-axis shows the time T.

As discussed herein, driving voltage pulse V₀ is applied by the voltage source 106 to drive (i.e., move) the dsDNA molecule 110 from the top fluidic chamber 130 into the Y-channel 140, though the stem 170, and to the junction 220 (i.e., temporarily stopping at the junction 220 because the electric field E₀ is not strong enough to break the base pair abutting the tip of the junction 220). For example, the chart 300 shows that the electric field E₀ (via driving voltage pulse V₀) is applied for time T₀ through T₁. Then, the higher voltage pulse V₁ is applied for time T₁ through T₂ resulting in higher electric field E₁, as shown in FIG. 3. Once the higher electric field E₁ breaks (i.e., unzips) the base pair that was previously positioned at the junction 220, the driving voltage pulse V₀ is again applied (for time T₂ through T₃) to drive (i.e., advance) the dsDNA molecule 110 to position (i.e., stop) the next base pair at the junction 220. The higher voltage pulse V₁ is again needed (and applied via voltage source 106 for time T₃ through T₄) to break this next base pair now positioned at the junction 220. This process repeats to ratchet the dsDNA molecule 110 through the Y-channel 140 one base (i.e., one nucleotide spacing) at a time, and results in the dsDNA molecule 110 being unzipped into the ssDNA molecule 112 and ssDNA molecule 114.

As shown in FIG. 3, a pulse with a higher electric field E₁ is applied to open one base-pair and thread two complimentary nucleotides into two branches respectively. By alternatingly applying the lower driving voltage pulse V₀ and the (base pair breaking) higher voltage pulse V₁, FIG. 1 shows how the two ssDNA strands 112 and 114 are in two branches 172 and 174 of the Y-channel 140 and shows the remaining dsDNA molecule 105 is in the stem 170 of the Y-channel 140. Each time the high voltage pulse V₁ is applied, the DNA molecule 110 moves forward by one nucleotide (i.e., by one base), and this is the nucleotide-by-nucleotide ratcheting. Note that motion of ssDNA in a CNT can be frictionless. Therefore, each ssDNA 112 and 114 can be easily driven by an electric field through the Y-CNT (140). It is noted that when turning off the biasing electric field (i.e., turning off the voltage source 106), hybridizing of two complementary ssDNA molecules 112 and 114 occurs resulting in reverse ratcheting. For example, the dsDNA molecule 110 moves in reverse which is back into the top fluidic chamber 130, when the voltage source 106 is turned off, and the again forms base pairs.

As one example, the energy required to break the hydrogen bond between the base pair of the dsDNA molecule 110 (at the junction 220) is about 2-3 k_(B)T, where k_(B) is the Boltzmann constant and T is the temperature.

An example driving voltage pulse V₀ to drive the dsDNA molecule 110 through the Y-channel 140 may be 0.1 volt, which results in the electric field E₀ and a downward driving force. The downward driving force (from cis. to trans.) does not break/unzip the base pair. The higher breaking voltage pulse V₁ may be 0.2 volts, applied for approximately 0.1 μs (micro-seconds).

When one (or both) of the ssDNA molecules 112 and 114 exits a channel branch (e.g., respective branch 172 and/or 174) and enters the bottom fluidic chamber 135, a sensor (e.g., pair of electrodes 150 as one sensor and a pair of electrodes 155 as another sensor) built on the solid surface of the membrane 101 and at the end of a channel branch (e.g., branches 172 and/or 174) can be used to detect/read each base in the ssDNA molecule 112 and/or ssDNA molecule 114. FIG. 4 illustrates the nanodevice 100 with sensors in the left branch 172 and the right branch 174 to respectively sequence the ssDNA molecule 112 and the ssDNA molecule 114 according to an embodiment. FIG. 4 is one example of how the single strands may be sequenced and other sequencing methods may be utilized to read bases of the single strands, as understood by one skilled in the art.

For example, a sensor can consist of the pair of electrodes 150 in the left branch 172, and when a DNA base is in the gap of these two electrodes 150, an ammeter 160 can measure the base-sensitive tunneling current when voltage of the voltage source 162 is applied. To increase the reading accuracy and efficiency, the nanodevice 100 can be used to sequence two complementary ssDNA strands 112 and 114 simultaneously in the DNA ratcheting machine 100, which is another benefit of the current design. For example, the base between the pair of electrodes 150 (or maybe the previous or subsequent base) may be complementary to the base (concurrently) between the pair of electrodes 155, and the complementary bases can be respectively sequenced via respective voltages sources 162 and 167 and respective ammeters 160 and 165.

For example, while the voltage source 162 applies voltage to the pair of electrodes 150 and while the voltage source 167 applies voltage to the pair of electrodes 155, the ammeter 160 measures the tunneling current through the base (of the ssDNA 112) in the gap between electrodes 150 in the branch 172, and the ammeter 165 measures the tunneling current through the complementary base (of the ssDNA 114) in the gap between electrodes 155 in the branch 174. Accordingly, the two complementary DNA strands 112 and 114 are simultaneously or near simultaneously sequenced while the dsDNA molecule 110 is being ratcheted as discussed herein. This helps to confirm the accuracy of the bases being read in FIG. 4 because the respective bases in branches 172 and 174 should be complementary.

Complementary is a property shared between two nucleic acid sequences, such that when they are aligned antiparallel to each other, the nucleotide bases at each position will be complementary. Two bases are complementary if they form base pairs. For DNA, adenine (A) bases complement thymine (T) bases and vice versa; guanine (G) bases complement cytosine (C) bases and vice versa. With RNA, it is the same except that uracil is present in place of thymine, and therefore adenine (A) bases complement uracil (U) bases.

FIG. 5 is a method 500 for ratcheting a double strand molecule (e.g., the dsDNA 110) through a Y-channel according to an embodiment. Reference can be made to FIGS. 1-4, 6, and 7. Various example may be for DNA but equally apply to RNA

The voltage source 106 (e.g., computer test setup 700) is configured (or controlled) to drive the double strand molecule 110 into a Y-channel 140 in a membrane 101 by a first voltage pulse (V₀) at block 505. The Y-channel 140 comprises the stem 170 and branches 172 and 174, and the branches 172 and 174 connect to the stem at the junction 220.

The voltage source 106 (e.g., computer test setup 700) is configured (or controlled) to slow the double strand molecule 110 at the junction 220 of the Y-channel 140 based on the first voltage pulse (V₀) being weaker than the force required to break a base pair of the double strand molecule 110 at block 510.

The voltage source 106 (e.g., computer test setup 700) is configured (or controlled) to split the double strand molecule 110 into the first single strand 112 and the second single strand 114 by driving the double strand molecule 110 into the junction 220 of the Y-channel 140 at a second voltage pulse (V₁) at block 515.

The method further includes sequencing the first single strand (e.g., ssDNA 112) one (e.g., left branch 172) of the branches, and sequencing the second single strand (ssDNA 114) in another one (e.g., right branch 174) of the branches. Sequencing the first single strand in the one of the branches comprises reading one base in the first single strand, and sequencing the second single strand in the other one of the branches comprises reading another base of the second single strand, where one base (between the pair of electrodes 150) on the first single strand (ssDNA 112) is complimentary to the other base (between the pair of electrodes 155) on the second single strand.

The method further includes simultaneously sequencing complementary bases of the first single strand and the second single strand respectively in the branches 172 and 174.

The membrane 101 can include a plurality of Y-channels 140 (and/or Y-channels 340 in any combination), each having a stem and branches such as shown in FIGS. 2 and 6. The Y-channel 140 (340) is a Y-shaped carbon nanotube.

The voltage source 106 is configured to (automatically, semi-automatically, and/or manually) alternatingly apply the first voltage pulse (V₀) for a first time period (e.g., time T₀ through T₁) and the second voltage pulse (V₁) for a second time period (e.g., time T₁ through T₂) until the double strand molecule 110 has been completely split into the first single strand (ssDNA 112) and the second single strand (ssDNA 114). The direction of the double strand molecule can be reversed (i.e., going from bottom fluidic chamber 135 to top fluidic chamber 130 (trans. to cis.)) through the membrane 101 by discontinuing (both) the first voltage pulse and the second voltage pulse applied by the voltage source 106.

FIG. 6 is an abbreviated version of the nanodevice 100 in which the membrane 101 comprises Y-channels 340 with multiple branches according to an embodiment. The Y-channel 340 has stem 350 a main left branch 351 and a main right branch 352. The main left branch 351 splits into a secondary left branch 353 and a secondary right branch 354. Similarly, the main right branch 352 splits into a secondary left branch 355 and a secondary right branch 356.

The following are example dimensions of the Y-channel 340. The stem 350 may have a width 305 (and/or diameter) of 5 nm. The main left branch 351 and the main right branch 352 may each have a width 310 (and/or diameter) of 3.2 nm.

The secondary left branch 353 and the secondary left branch 355 may each have a width 315 (and/or diameter) of 2 nm.

The secondary right branch 354 and the secondary right branch 356 may each have a width 320 (and/or diameter) of 2 nm.

Although not shown so as not to obscure the figure, the branches 353, 354, 355, and 356 may each have its own sensor (i.e., electrode pair connected to a voltage source and ammeter) for reading the single bases.

As the stem 350 of Y-channels 340 is made large enough for dsDNA 110 to get in, the dsDNA 110 may go through either main left branch 351 or main right branch 352. If the dsDNA 110 enters main left branch 351, the ratcheting of dsDNA 110 occurs at the junction of the channels for the secondary left branch 353 and secondary right branch 354. Two DNA strands will be unzipped, and a single strand enters secondary left branch 353 and the complementary single strand enters secondary right branch 354, respectively (as discussed above in FIGS. 1-5).

FIG. 7 illustrates an example of a computer 700 (e.g., as part of the computer test setup for testing and analysis) which may implement, control, and/or regulate the voltage of the voltage source 106, and measurements of the ammeters 160 and 165 as discussed herein.

Various methods, procedures, modules, flow diagrams, tools, applications, circuits, elements, and techniques discussed herein may also incorporate and/or utilize the capabilities of the computer 700. Moreover, capabilities of the computer 700 may be utilized to implement features of exemplary embodiments discussed herein. One or more of the capabilities of the computer 700 may be utilized to implement, to connect to, and/or to support any element discussed herein (as understood by one skilled in the art) in FIGS. 1-6. For example, the computer 700 which may be any type of computing device and/or test equipment (including ammeters, voltage sources, connectors, etc.). Input/output device 770 (having proper software and hardware) of computer 700 may include and/or be coupled to the nanodevices and structures discussed herein via cables, plugs, wires, electrodes, patch clamps, etc. Also, the communication interface of the input/output devices 770 comprises hardware and software for communicating with, operatively connecting to, reading, and/or controlling voltage sources, ammeters, and current traces (e.g., magnitude and time duration of current), etc., as discussed herein. The user interfaces of the input/output device 770 may include, e.g., a track ball, mouse, pointing device, keyboard, touch screen, etc., for interacting with the computer 700, such as inputting information, making selections, independently controlling different voltages sources, and/or displaying, viewing and recording current traces for each base, molecule, biomolecules, etc.

Generally, in terms of hardware architecture, the computer 700 may include one or more processors 710, computer readable storage memory 720, and one or more input and/or output (I/O) devices 770 that are communicatively coupled via a local interface (not shown). The local interface can be, for example but not limited to, one or more buses or other wired or wireless connections, as is known in the art. The local interface may have additional elements, such as controllers, buffers (caches), drivers, repeaters, and receivers, to enable communications. Further, the local interface may include address, control, and/or data connections to enable appropriate communications among the aforementioned components.

The processor 710 is a hardware device for executing software that can be stored in the memory 720. The processor 710 can be virtually any custom made or commercially available processor, a central processing unit (CPU), a data signal processor (DSP), or an auxiliary processor among several processors associated with the computer 700, and the processor 710 may be a semiconductor based microprocessor (in the form of a microchip) or a macroprocessor.

The computer readable memory 720 can include any one or combination of volatile memory elements (e.g., random access memory (RAM), such as dynamic random access memory (DRAM), static random access memory (SRAM), etc.) and nonvolatile memory elements (e.g., ROM, erasable programmable read only memory (EPROM), electronically erasable programmable read only memory (EEPROM), programmable read only memory (PROM), tape, compact disc read only memory (CD-ROM), disk, diskette, cartridge, cassette or the like, etc.). Moreover, the memory 720 may incorporate electronic, magnetic, optical, and/or other types of storage media. Note that the memory 720 can have a distributed architecture, where various components are situated remote from one another, but can be accessed by the processor 710.

The software in the computer readable memory 720 may include one or more separate programs, each of which comprises an ordered listing of executable instructions for implementing logical functions. The software in the memory 720 includes a suitable operating system (O/S) 750, compiler 740, source code 730, and one or more applications 760 of the exemplary embodiments. As illustrated, the application 760 comprises numerous functional components for implementing the features, processes, methods, functions, and operations of the exemplary embodiments.

The operating system 750 may control the execution of other computer programs, and provides scheduling, input-output control, file and data management, memory management, and communication control and related services.

The application 760 may be a source program, executable program (object code), script, or any other entity comprising a set of instructions to be performed. When a source program, then the program is usually translated via a compiler (such as the compiler 740), assembler, interpreter, or the like, which may or may not be included within the memory 720, so as to operate properly in connection with the O/S 750. Furthermore, the application 760 can be written as (a) an object oriented programming language, which has classes of data and methods, or (b) a procedure programming language, which has routines, subroutines, and/or functions.

The I/O devices 770 may include input devices (or peripherals) such as, for example but not limited to, a mouse, keyboard, scanner, microphone, camera, etc. Furthermore, the I/O devices 770 may also include output devices (or peripherals), for example but not limited to, a printer, display, etc. Finally, the I/O devices 770 may further include devices that communicate both inputs and outputs, for instance but not limited to, a NIC or modulator/demodulator (for accessing remote devices, other files, devices, systems, or a network), a radio frequency (RF) or other transceiver, a telephonic interface, a bridge, a router, etc. The I/O devices 770 also include components for communicating over various networks, such as the Internet or an intranet. The I/O devices 770 may be connected to and/or communicate with the processor 710 utilizing Bluetooth connections and cables (via, e.g., Universal Serial Bus (USB) ports, serial ports, parallel ports, FireWire, HDMI (High-Definition Multimedia Interface), etc.).

In exemplary embodiments, where the application 760 is implemented in hardware, the application 760 can be implemented with any one or a combination of the following technologies, which are each well known in the art: a discrete logic circuit(s) having logic gates for implementing logic functions upon data signals, an application specific integrated circuit (ASIC) having appropriate combinational logic gates, a programmable gate array(s) (PGA), a field programmable gate array (FPGA), etc.

The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” and/or “comprising,” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one more other features, integers, steps, operations, element components, and/or groups thereof.

The corresponding structures, materials, acts, and equivalents of all means or step plus function elements in the claims below are intended to include any structure, material, or act for performing the function in combination with other claimed elements as specifically claimed. The description of the present invention has been presented for purposes of illustration and description, but is not intended to be exhaustive or limited to the invention in the form disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the invention. The embodiment was chosen and described in order to best explain the principles of the invention and the practical application, and to enable others of ordinary skill in the art to understand the invention for various embodiments with various modifications as are suited to the particular use contemplated

The flow diagrams depicted herein are just one example. There may be many variations to this diagram or the steps (or operations) described therein without departing from the spirit of the invention. For instance, the steps may be performed in a differing order or steps may be added, deleted or modified. All of these variations are considered a part of the claimed invention.

While the preferred embodiment to the invention had been described, it will be understood that those skilled in the art, both now and in the future, may make various improvements and enhancements which fall within the scope of the claims which follow. These claims should be construed to maintain the proper protection for the invention first described. 

What is claimed is:
 1. A method for ratcheting a double strand molecule, the method comprising: driving the double strand molecule into a first Y-channel and a second Y-channel of a membrane by a first voltage pulse, the first Y-channel includes a first stem, a first left branch, and a first right branch formed in the membrane, the first left and right branches being connected to the first stem at a first junction; wherein the second Y-channel includes a second stem, a second left branch, and a second right branch formed in the membrane, the second left and right branches being connected to the second stem at a second junction, wherein the second stem of the second Y-channel is connected to the first left branch of the first Y-channel such that the first left branch feeds into the second Y-channel, and wherein the second junction comprises a sharp end configured to separate baase pairs; slowing the double strand molecule at the first junction of the first Y-channel based on the first voltage pulse being weaker than a force required to break a base pair of the double strand molecule; and driving the double strand molecule into the sharp end of the second junction to thereby split the double strand molecule into the first single strand and the second single strand using a second voltage pulse.
 2. The method of claim 1, wherein the double strand molecule is deoxyribonucleic acid or ribonucleic acid.
 3. The method of claim 1, wherein the membrane comprises a plurality of Y-channels, each having its stem and corresponding branches.
 4. The method of claim 1, wherein the first and second Y-channels are Y-shaped carbon nanotubes.
 5. The method of claim 1, further comprising alternatingly applying the first voltage pulse for a first time period and the second voltage pulse for a second time period until the double strand molecule has been completely split into the first single strand and the second single strand.
 6. The method of claim 1, further comprising reversing a direction of the double strand molecule through the membrane by discontinuing the first voltage pulse and the second voltage pulse.
 7. The method of claim 1, wherein a difference in diameter from the second stem to the second left and right branches is about 1 nm.
 8. The method of claim 7, wherein a difference in diameter from the first stem to the second stem is about 2 nm. 